dvipdfmx.cfg in dvipdfm\config contains a reference to the map file kanjix.map:
% the following file is generated by updmap(-sys) from the % KanjiMap entries in the updmap.cfg file. f kanjix.map
The updmap of texlive creates this map automatically in fonts/map/dvipdfmx/updmap. (The default kanjix.map is empty, but there is an option in updmap.cfg to change this).
The updmap / initexmf --mkmaps command of miktex doesn't create the map file automatically and so it is missing and every xetex run issues a (rather harmless) warning which nevertheless disturbs people a bit. Please add a dummy kanjix.map somewhere in fonts/map/dvipdfmx or desactivate the reference in the cfg (or change updmap).